Objectives Auditory system function and attention are examined in the rhesus monkey as a model of childhood lead exposure. Peripheral and higher order auditory processes are evaluated using behavioral and electrophysiological techniques. Work during the previous grant period revealed significant and persistent effects on auditory function in a nonhuman primate model (the rhesus monkey) of childhood lead exposure. We have demonstrated evidence for cochlear pathology in the two rhesus monkeys with greatest lead exposure. In addition, auditory evoked responses were delayed and measures of attention in an auditory detection reaction time test differed when exposed monkeys were compared with controls. These effects represent enduring and probably irreversible effects on nervous system function since the monkeys were 11-13 yrs old at the time of testing. Lead exposure was during early development and body burdens of lead had been at undetectable levels for many years at the times of these evaluations. Other research from this lab and by others has demonstrated effects of early exposure to lead and to other agents on auditory-based attentional processes in animal models of childhood lead exposure and in children. The attentional processes evaluated in these studies underlie many of the more global cognitive abnormalities that have been associated with childhood lead exposure. In addition to attention deficit disorder and other attentional problems, these include IQ (especially verbal IQ), speech perception, language production, reading, and school problems, effects of lead on auditory system processing are of particular importance given that spoken language is the primary route by which learning occurs in young children. A better understanding of the adverse consequences of early lead exposure on auditory based attentional processes would facilitate the design of therapeutic interventions and special education programs for children and adults who are known to have experienced early lead exposure. The aim of this research is to further characterize possible lead-associated deficits in auditory function and to further delineate auditory-based attentional deficits associated with lead. Frequency specific thresholds, frequency tuning, and nonlinear processes will be evaluated electrophysiologically. A broad range of attentional processes will be evaluated behaviorally. These include the simple measures of attention which previously yielded effects of lead in our lab and which will be evaluated under different conditions of task complexity and attentional demand. Cued attention, temporal processing and directed attention also will be evaluated behaviorally as will distractibility and tracking. The efficacy of procedural changes and pharmacological interventions to attenuate effects of lead on performance also will be examined in the behavioral and physiological studies. Subjects for the proposed studies are 17 14-yr old monkeys. Lead exposure was during early development and the monkeys are now adult, so evaluation of enduring and possibly irreversible effects is the ultimate goal. Lead exposure parameters and experimental histories over the life span. Key Words Lead, Monkeys, Hearing, Electrophysiological, Cognition, Auditory Processing